The present invention relates to spatial light modulators and holographic recording/reproducing apparatuses, and more particularly to a spatial light modulator and holographic recording/reproducing apparatus capable of suppressing the useless consumption of material sensitivity of a holographic recording medium and preventing against crosstalk.
The holographic recording/reproducing method is known as one method for realizing recording of information with high density. In the usual holographic recording/reproducing method, the signal beam added, two-dimensionally, with data is superposed with a reference beam at within a recording medium. The interference fringe formed is written, to thereby record the information. The data thus recorded on the holographic recording medium can be reproduced by irradiating a reference beam. The reference beam irradiated to the recording medium is diffracted by the grating of interference fringe, thereby causing a reproducing image to be detected and reproducing data. On such a recording medium, the data added on the signal beam can be reproduced at one time by the incidence of a reference beam, thus realizing high-speed reproduction.
The signal beam and reference beam, usually using a laser beam having Gaussian distribution, involves a problem of non-uniformly consuming the material sensitivity. Hence, the laser beam is preferably uniform throughout the beam spot.
JP-A-08-314364 shows a known method of irradiating while scanning a thin beam to an SLM (Spatial Light Modulator). This is equivalent, as the whole SLM, to the irradiation of a laser beam having a uniform intensity distribution within the spot, because the same intensity of beam is irradiated to each pixel of the SLM. Meanwhile, “Holographic data storage” (J. Ashley and ten others, IBM Journal of Research and Development, May 2000, Vol. 44, No. 3, p 348.) also shows a method that the input beam having Gaussiam distribution is reorganized in intensity by using a pair of aspherical optical element to thereby output a uniform intensity of beam within a predetermined area.
However, in the foregoing method of irradiating while scanning a thin beam to the SLM, it takes long time in irradiating the beam throughout the SLM entirety, thus making difficult to realize high-speed recording and reproduction. Meanwhile, in the method of using a pair of non-linear optical element, such an optical element must be provided, increasing the size of the entire optical system. Besides, application is only to a particular intensity distribution, resulting in a fear of insufficient degree of waveform shaping.